Prospect of conflict with China over islands in East China Sea propels cartoon novels selling in millions

TOKYO—On a stormy night, three mysterious figures clamber onto an uninhabited island in the East China Sea. Tensions spiral upward from there until China invades several Japanese islands, triggering Tokyo’s first use of military force since World War II in a fierce battle on land, air and sea.

It is all fiction, laid out in a series of manga cartoon novels called “Aircraft Carrier Ibuki” that has sold more than three million copies in Japan by presenting a plausible tale of the nation’s military future. Coming next: a movie...